https://hal.archives-ouvertes.fr/hal-02381264/document

Experimental modelling of urban flooding: a review.

A first approach to the experimental study of the dividing flow in steep street crossings is presented. A scale model of a street crossing has been built and a series of tests has been conducted for studying the flow pattern in the crossing when the flow in the streets is supercritical. It has been found that the inflow power ratio at the entrance of the crossing can be used as a non-dimensional parameter for predicting the flow distribution as well as the flow pattern. On the basis of these relationships a one-dimensional formulation can be developed in order to predict the dividing flow in crossings.

Experimental study of the dividing flow in steep street crossings

High bed-shear stress resulting from secondary flows and velocity increase at a channel junction cause local erosion and deposition in natural rivers and earth-lined channels. Herein, the scour patterns at the junction of two loose bed channels were studied under clear-water conditions. The main dimensionless variables are the angle between the two approach flow branches, the discharge and width ratios of the tributary to the downstream channel branches, and the ratio of the mean downstream velocity to the threshold velocity. The results indicate that the position of the maximum scour depth temporally moves to the outer wall and upstream to the main channel, as affected by the dimensionless variables. The effects of these variables are given in graphs and are expressed with a formula for maximum scour depth.

Local scour at open-channel junctions

This paper proposes a new model to determine the head losses at confluences in one-dimensional models of open channel networks, making use of a momentum conservation approach Momentum conservation has been applied in several theoretical models for confluence head losses, giving satisfactory results in general However, for larger confluence angles between the main channel and the incoming tributary, the model accuracy diminished Many authors identified that a correct estimation of the tributary momentum contribution is a prerequisite for accurate results This work reports on the development and application of a theoretical model for the tributary momentum contribution, based on similarities with the flow upstream of a circular bend in a straight open channel It describes the two-dimensional depth-averaged flow features in the tributary under the assumption of a 90° angle confluence in which all channels have equal widths, in order to obtain the resulting momentum contribution The proposed mod

Modelling of the tributary momentum contribution to predict confluence head losses

In this paper, a comparison between the 1D and 2D approaches for simulating combining flows at open-channel junctions is presented. The two approaches are described allowing for a full comprehension of flow modelling. For flows in an open-channel network, mutual effects exist among the channel branches at a junction. Therefore, the 1D Saint-Venant equations for the branch flows are supplemented by various junction models. The existing models are of empirical nature and depend on the flow regime and thus are not practical in all cases. The numerical approximation of the two approaches is performed by the Runge–Kutta discontinuous Galerkin scheme and tested using defined flow problems to illustrate the results of the two approaches. Comparisons are conducted for supercritical, transitional and subcritical flows, indicating the validity range of the 1D approach and the advantages of the 2D approach.

Comparative study of 1D and 2D flow simulations at open-channel junctions

On the basis of energy and continuity equations a simple one-dimensional formulation was proposed to predict the transitional flow at an open-channel junction. An empilical relation between the junction losses, the junction angle, and the discharge ratio was suggested which agrees well with the experimental results. The results calculated by the present formulation for the depth ratio were compared with the results of earlier one-dimensional formulations and experiments. It is found that the present results coincide better with experiments than those of others.

LIUYa-kun

Papers

Transitional flow in channel junctions